In biomeasurement using light, an apparatus for measuring the activity of a living body by using visible to near infrared light is disclosed in, e.g., Japanese Patent Application Laid-Open No. 57-115232 or Japanese Patent Application Laid-Open No. 63-275323. In addition, an invention pertaining to image measurement technology for the activity of a brain (optical topography (R)), which has been achieved through the application of the present principle of measurement, is proposed in Japanese Patent Application Laid-Open No. 9-98972.
Each of these inventions irradiates a living body with light by using an optical wave-guiding device represented by an optical fiber or the like and collects and measures the light scattered within the living body (hereinafter shortly referred to as the living-body scattered light) at a position several millimeters to several centimeters apart. From the measured intensity of the living-body scattered light, the concentration of a substance of light absorption within the living body represented by oxygenated hemoglobin or deoxygenated hemoglobin or a value corresponding to the concentration is determined. In determining the concentration of the substance of light absorption or the value corresponding to the concentration, the light absorption characteristic of the objective substance of light absorption, which corresponds to the wavelength of the irradiated light, is used. In the case of measuring a deep portion in a living body, light with a wavelength in the range of 650 nm to 1300 nm, which is high in living body penetration, is used normally.
In biophotometry, a device for irradiating a subject (living body) with light (hereinafter referred to as the device for light irradiation) and a device for collecting light propagated through the inside of the living body (hereinafter referred to as the device for collection of light) are provided. As the device for light irradiation and the device for collection of light, an optical wave-guide represented by an optical fiber or a bundle of optical fibers is provided in most cases. A pair of optical wave-guides for light irradiation and for collection of light form a minimum unit representing one measurement position (hereinafter referred to as the light-irradiation/collection-of-light pair). An apparatus for performing image measurement for a living body with the setting of a plurality of the minimum units is proposed in Japanese Patent Application Laid-Open No. 9-98972.
It is to be noted that the distance between the light irradiation position and the collection of light position in the light-irradiation/collection-of-light pair (hereinafter referred to as the light-irradiation/collection-of-light intra-pair distance) varies with the area or depth of a region to be measured. To respond to the variation, Japanese Patent Application Laid-Open No. 9-98972 proposes an arrangement in which the optical wave-guides for light irradiation and the optical wave-guides for collection of light are alternately arranged at the points of a square lattice such that the individual light-irradiation/collection-of-light intra-pair distances are equal. If the arrangement is used, each of the optical wave-guides is used commonly by a plurality of the light-irradiation/collection-of-light pairs so that image measurement is accomplished with a smaller number of optical wave-guides. This allows short-time attachment of the optical wave-guides to a living body.